Oxygen barrier coating composition containing trimethoxysilyl functional pentadienoate

Abstract: Composite films which exhibit low oxygen transmission rates comprise a silane resin coated on a plastic substrate which is then cured by ultraviolet radiation. For the silane coating, this invention relies on a class of organosilicon compounds derived from 1) organohydrogensilanes or organohydrogensiloxanes and 2) propargyl esters of carboxylic acids containing a terminal aromatic hydrocarbon radical, where the carbopropynoxy group of the ester and the aromatic hydrocarbon radical are separated by at least two adjacent ethylenically unsaturated carbon atoms. If more than two of these carbon atoms are present, they form a sequence of conjugated ethylenic double bonds which allows the polymer to cross-link upon exposure to ultraviolet radiation.

Description: This invention relates to composite films generally and composite films for applications requiring low oxygen transmission rates in particular. Packages allowing significant penetration of oxygen or other gases are undesirable where gas transmission contributes to the decay of the packaged product. For example, the development of packages having low oxygen transmission rates, i.e., high oxygen barrier properties, has long been a desirable objective because low gas permeability food packages increase the shelf life of packaged food products. Packages with low oxygen transmission rates also have utility for packaging other oxygen sensitive materials, such as oxygen activated sealants. Longer shelf life increases inventory efficiency for distributors and reduces the likelihood that the consumer will accidently purchase a contaminated product. For a plastic film to qualify for food packaging applications, the film has to have low oxygen permeability at low relative humidity and also at high relative humidity since the packed food may be stored in either environment. Unfortunately, most commercially available plastic films cannot meet these two requirements simultaneously. The ideal film will have both low oxygen permeability and will also be insensitive to relative humidity. Our invention solves these problems by introducing a silicone treated plastic film which exhibits excellent low gas transmission characteristics both at 0% relative humidity and at 85% relative humidity. The related prior art is represented by US-A(s) 5,077,135 and 5,096,738 which disclose methods of imbuing polymer films with gas impermeable surface characteristics using silane compounds and cross-linkers to produce gas and related barrier characteristics. The present invention teaches the preparation of composite films which exhibit low oxygen transmission rates. These films comprise a silane resin coated on a plastic substrate and then cured by ultraviolet radiation. For the silane coating, our invention relies on a class of organosilicon compounds derived from 1) organohydrogensilanes or organohydrogensiloxanes and 2) propargyl esters of carboxylic acids containing a terminal aromatic hydrocarbon radical, characterized by the carbopropynoxy group of the ester and the aromatic hydrocarbon radical being separated by at least two adjacent ethylenically unsaturated carbon atoms. If more than two of these carbon atoms are present, they form a sequence of conjugated ethylenic double bonds which allows the polymer to cross-link upon exposure to ultraviolet radiation. The silicone resin is formed from an organosilane having the general formula (1) Q(R 1 O) 3 Si where Q represents the radical R 2 (CH=CH) n -CH=CR 3 C(O)R 5 -, each R 1 is individually selected from unsubstituted and substituted monovalent hydrocarbon radicals; R 2 represents an aryl, alkoxyaryl or alkaryl radical; R 3 is selected from -C≡N and -C(O)OR 4 where R 4 is hydrogen or an unsubstituted monovalent hydrocarbon radical selected from the same group as R 1 , R 5 is -O(CH 2 ) a CH=CH- or -NR 6 -(CH 2 ) b -; R 6 is a hydrogen or hydrocarbon radical having from 1 to 6 carbon atoms, a is 1 to 5, b is 3 to 6 and n is 0 or a positive integer, with the proviso that n can be 0 only when R 2 represents naphthyl radical. While the invention is susceptible of many different forms, there is described herein preferred and alternate embodiments of the invention. It should be understood, however, that the present disclosure is an exemplification of the principles of the invention. The preferred embodiment of the invention is a film consisting of a plastic substrate having disposed thereon a coating of silicone resin formed from a silane solution. The plastic material is typically a commercially available polyolefin, such as polyethylene, polypropylene, polyethyleneterephthalate or a polyester, such as MYLAR™ available from DuPont, (Wilmington, Delaware). The substrate may be any thickness, but will likely be at least 25 micrometers thick. In US-A 5,136,065, the platinum-catalyzed hydrosilylation reaction of an organohydrogensiloxane occurs exclusively at the propargyl group, resulting in a high yield of the desired product containing units of the formula R 2 (CH=CH) n -CH=CR 3 C(O)R 5 Si(OR 1 ) 3 (where R 5 is -O(CH 2 ) a CH=CH- and a, R 2 , n, R 3 and R 1 are defined as above). In contrast, the expected mixture of products resulting therein from the hydrosilylation reaction should be at the carbon-carbon double bonds or at the carbonyl portion of the carboxyl group. The organosilicon compounds of this invention undergo an intermolecular coupling reaction in the presence of ultraviolet radiation in the range of 300 to 400 nm that is believed to involve formation of cyclobutane rings by pairs of ethylenically unsaturated carbon atoms on adjacent molecules of the compound. This reaction is simply depicted as: The substituent represented by R 3 in the present compounds can be a cyano (-C≡N) group or a group represented by the formula -C(O)OR 4 where R 4 is hydrogen or an unsubstituted monovalent hydrocarbon radical. Unsubstituted monovalent hydrocarbon radicals that can be represented by R 1 and R 4 include alkyl radicals containing from 1 to 10 carbon atoms such as methyl, ethyl and propyl; cycloalkyl radicals such as cyclohexyl; aryl such as phenyl; alkaryl such as tolyl and xylyl and aralkyl such as benzyl. Most preferably, R 1 is methyl, phenyl or 3,3,3-trifluoropropyl and R 4 is hydrogen. R 2 represents an aryl, alkoxyaryl or alkaryl radical such as phenyl, o-, m- or p-methoxyphenyl, naphthyl or tolyl. In preferred embodiments of our compounds, R 2 is phenyl, o-, m- or p-methoxyphenyl or naphthyl and n is 0 or 1, this preference being based on the availability of the starting materials and the high yield of desired product without undesirable by-products when the propargyl ester is prepared using the Knoevenagel condensation reaction of US-A 5,136,065. While the examples below set forth the oxygen transmission rates of the coated films, the silane coating disclosed herein can also be used in a multi-layer sandwich configuration. Such configurations are disclosed in a commonly assigned application EP Application No. 94 303 290.4 filed May 6, 1994. The measurements of oxygen permeability for each of the composite films discussed in the following examples were made using pure oxygen on a MOCON OX-TRAN™ 100A tester (Modern Controls, Inc., Minneapolis, MN) according to ASTM F1307-90 at 32.5°C. "Dry" readings were taken in an environment where the relative humidity was 0 percent and the "wet" readings were taken in an environment where the relative humidity was greater than 85 percent. Corona treatment of the substrates was done by passing the substrate under a Tesla Coil for approximately one-half second. A silane compound, N-3-trimethoxysilylpropyl 2-cyano-5-phenyl-2,4-pentadienoamide, (hereinafter, "CPPDATMS") was prepared by mixing equal molar amounts of methyl 2-cyano-5-phenyl-2,4-pentadienoate (40 g) and 3-aminopropyltrimethoxysilane (33.69 g) together, then adding an equal weight of toluene (74 g). The mixture was heated at 85°C. until no starting material was shown in the IR spectra of the admixture. Removal of the toluene under reduced pressure afforded a yellow waxy solid. After preparation of the silane compounds described above, three films were made from corona treated low density polyethylene (LDPE) substrates of 100 micrometers thickness. To make the film, the silane compound was dissolved in a solvent, such as acetone or methanol, itaconic acid and water. Then the corona treated LDPE film was coated on both sides. After coating, the light yellow, opaque coated film was allowed to dry for several minutes, then subjected to UV cure. The UV cure took place under an OAI™ Model 30 near UV flood exposure system, (Optical Associates, Inc., Milpitas, Ca.) at 15 mw/cm 2 . Irradiation time was 60 seconds for each side of the film which resulted in a clear, colorless film. Coating thickness of the silane layer of each film was estimated to be between 1 and 2 micrometers. The table below shows the oxygen transmission data for various combinations of CPPDATMS in solution, the solvent amount and type, if the coated substrate was cured with UV irradiation and the oxygen transmission rates, both wet and dry. Oxygen Permeability (OP in cm 3 /m 2 /day) of Trialkoxysilyl Functional Pentadienoate Coated LDPE Films SOL. WT(g) SOL WT(G) H 2 O WT(g) Cure OP DR OP WET CONTROL NONE NONE NONE 2300 --- CPPDATMS 10 MEK 90 4 UV ---- 1380 CPPDATMS 5 MEK 90 4 UV 255 245 IA 5 CPPDATMS 5 MEK 90 4 -- --- 345 IA 5 CPPDATMS 5 MeOH 90 4 UV 91 92 IA 5 MEK = Methyl Ethyl Keytone MeOH = Methanol IA = Itaconic Acid The data in the table shows that the combination of CPPDATMS in 5 g of itaconic acid, in methanol (MeOH) and water has the most favorable overall improvements in oxygen transmission rates, reducing same by 20 fold over the untreated control group which had dry oxygen transmission rates of 2300 cm 3 /m 2 /day. More importantly, the low oxygen permeability was maintained over a wide range of relative humidity - a property that is critical for the packaging application. However, the other films with the CPPDATMS coating also performed well, each showing one order of magnitude decrease in oxygen transmission rates over the control. The foregoing specification describes only the preferred embodiment and the alternate embodiments of the invention. Other embodiments may be articulated as well. It is expected that skilled persons will perceive differences which, while differing from the foregoing, do not depart from the invention as herein described and claimed.

Claims: A silane coating composition comprising: (A) an organosilicon compound selected from silanes corresponding to the molecular formula Q(R 1 O) 3 Si where Q represents the radical R 2 (CH=CH) n -CH=CR 3 C(O)R 5 -, each R 1 is individually selected from unsubstituted monovalent hydrocarbon radicals; R 2 represents an aryl, alkoxyaryl or alkaryl radical; R 3 is -C≡N or -C(O)OR 4 where R 4 is hydrogen or an unsubstituted monovalent hydrocarbon radical selected from the same group as R 1 , R 5 is -O(CH 2 ) a CH=CH-or -NR 6 -(CH 2 ) b -; R 6 is a hydrogen or hydrocarbon radical having from 1 to 6 carbon atoms, a is 1 to 5, b is 3 to 6 and n is 0 or a positive integer, with the proviso that n can be 0 only when R 2 represents a naphthyl radical; (B) itaconic acid; (C) water; and (D) a solvent. A method for producing a silane coated substrate comprising: (I) coating a plastic substrate with the silane coating composition of claim 1; and then (II) curing the silane solution to a silicone resin with ultraviolet light. The coating composition of claim 1 wherein the solvent is methanol or methyl ethyl ketone. The coating composition of claim 1 wherein said silane solution is made from the following reactants comprising: (a) propargyl 2-cyano-5-phenyl-2,4,-pentadienoate; (b) toluene; (c) a platinum catalyst; and (d) trimethoxy silane. The coating composition of claim 1 wherein said silane solution is made from the following reactants comprising: (a) methyl 2-cyano-5-phenyl-2,4-pentadienoate; (b) 3-aminopropyltrimethoxysilane; and (c) toluene.

Inventors: LEE CHI-LONG, YEH MING-HSIUNG, LEE, CHI-LONG, YEH, MING-HSIUNG
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1994
Main classification: C09D4
IPC codes: C09D4, C08F222, C08F230, C08J7, C09D5, C08G61